1. Field of Invention
This invention generally relates to fiber optics and, more particularly, to optical communications systems or components thereof which utilize a fiber splice.
2. Description of Related Art
Conventional splicing operations and equipment are designed to minimize or eliminate optical signal attenuation. To that end, conventional splicing machines are designed to bring the two fibers into as perfect an alignment as possible. This goal of achieving optimum alignment between the fibers is met by utilizing various detectors and fine alignment control functions so that the fibers are aligned. Typically, the respective optical axes are aligned first and then the fibers are brought together so that their ends are in direct contact.
Conventional splicing machines utilize an electric arc to fuse the fibers. Such machines permit an operator to set fusing current, fusing time and fine tune fiber alignment to achieve the best alignment possible between the fibers. Such conventional splicing machines are designed to minimize the insertion loss or attenuation of the resulting splice by, for example, accurately aligning the fibers. These conventional splicing machines may be programmed according to various recipes that specify optimum fusing currents and fusing times for a variety of fiber types, core diameters and other fiber properties.
Such conventional splicing machines also permit an operator to intentionally misalign the fibers in a crude effort to perform an attenuating splice. Using various recipes similar to those mentioned above, an operator can construct an attenuating splice. This conventional attenuating splice operation requires a high degree of operator experience to choose the proper parameters such as fusion time and current. Furthermore, these operations are labor intensive and include typing in the large number of parameters at each step. The success rate also varies with the skill of the operator, machine condition, and environmental conditions. Even with an experienced operator and ideal conditions, these conventional techniques cannot provide an accurate attenuation value.
Various other conventional techniques exist for constructing attenuating splices. Gleason et al. (U.S. Pat. No. 4,557,557), for example, heats aligned optical fiber ends until they are in a plastic state. Then, the fiber ends are physically distorted by axial movement of one of the fiber ends. The amount of movement is controlled according to a measured optical loss across the splice. The fusion splice formed by this technique imposes a lumped optical loss value between the fiber ends. Yamamoto, et al. (U.S. Pat. No. 4,884,859) also heats aligned optical fiber ends to a temperature sufficient to soften the materials and then applies a tension and/or twist to the fiber to thereby form an optical attenuation area having fine cracks that scatter light. A major shortcoming of such techniques is the amount of attenuation is very difficult to control.
Forrester (U.S. Pat. No. 5,142,603) is another example of constructing a fusion splice with a controlled attenuation. Forrester fuses the ends of aligned fiber ends with heat. Once fused, the heat is continued for a time period sufficient to cause dopant to migrate out of the core and result in a desired attenuation.
Lin, et al. (U.S. Pat. No. 5,398,296) constructs a mode filter overlapping the fiber ends such that the fiber ends are parallel and overlapping. These overlapping fiber ends are then welded. Lin slightly separates the fibers to pull and narrow the welded portion. As the fibers are being separated, a power meter is monitored. When the readout reaches an object value, e.g. 3 dB, the process is stopped and the fibers are cooled. A material having a high index of refraction is then applied to the welded portion to form a mode filter.
Emmons, et al. (U.S. Pat. No. 5,588,087) constructs an overlapping fusion attenuator by overlapping two fiber ends to define an overlapped portion of the fibers. Heat is then applied to the overlapped portion by energizing an electric arc for about one second. The transmission loss is then measured and, if greater than a desired loss, the electric arc is turned on again for the same time period. As a result, the cores move closer together in the overlapped portion which results in a reduced transmission loss. This technique has serious shortcomings and can only produce at attenuation of greater than 10 dB. Alternative embodiments produce lower attenuation values by moving the fibers relative to one another in much the same way as described above to change the attenuation value.
The invention adds or otherwise produces a highly-controlled amount of attenuation in a fiber splice during the fiber splicing process. This process includes intentionally misaligning fiber cores during the splicing operation. Such intentional misalignment increases the insertion loss of the resulting splice.
In addition, the method disclosed here accurately controls the amount of attenuation introduced in the fiber splice. The degree of control is quite excellent and allows the manufacture of attenuating splices having an insertion loss that is controlled within +/xe2x88x920.25 dB and, preferably, within +/xe2x88x920.1 dB or less.
To this end, the inventive methods control the total amount power applied to the fibers during the fusing process. When utilizing an electric arc as the energy source, the invention may control the amount of power by controlling the driving current applied to the arc.
The inventive methods may exercise this control in a so-called power control mode or shut-down mode wherein the driving current is applied until the measured insertion loss is within a margin of the desired insertion loss value. As the hot splice cools, the insertion loss decreases and will settle at a value close to the desired insertion loss value. The shut-down mode operates while the fiber is energized and connected to a power meter. By monitoring the power meter, the method can determine when the insertion loss is within the desired margin and then shut down the energy source fusing the fibers.
The inventive method may also utilize an energy control mode or repeat mode either alone or in conjunction with the shut-down mode. The repeat mode changes the energy applied to the fibers during the splicing operation. When utilizing an electric arc as the energy source, the invention may control the driving current as well as the time the driving current is applied to fuse the fibers. The fused fibers are preferably allowed to cool and then a reading is taken of the insertion loss. If the insertion loss is not acceptable, then the process is repeated until the insertion loss is within the desired range.
With any one of these methods, the invention can eliminate conventional optical attenuators. Such conventional optical attenuators are relatively expensive, discrete components and the elimination thereof would reduce the cost and complexity of the resulting optical circuit and increase reliability. By eliminating conventional optical attenuators, the invention also eliminates at least two splices (or connectors) that were previously used to put the attenuator into the fiber line. System reliability is increased by reducing the number of separate components in the system.
A more significant advantage of the invention is that conventional attenuators are only available in fixed integer values such as 1 dB, 5 dB, and 10 dB. Fine tuning the attenuation of a given optical circuit is impossible with such conventional attenuators. In contrast, the invention permits an optical circuit attenuation to be fine tuned to non-integer values.
Furthermore, the attenuation can be designed directly into the optical circuit. Because splices are quite common and provided at myriad locations in an optical circuit, the invention can be utilized to fine tune the attenuation at any of these locations. A fiber could also be cut and spliced for the sole purpose of adding a desired, precisely controlled attenuation at any point in the fiber. In other words, this unique splicing process can be utilized to introduce controlled amounts of attenuation at selected splice points in the fiber line thereby providing industry with new and useful techniques. The degree of control and accuracy of the resulting attenuation provides significant advantages when compared with conventional devices and techniques.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.